Look at the 1, 2, & 3 star reviews. . .those people are commenting primarily on the shipping, or they're unenthusiastic students who have left one-line reviews.
I'm an English instructor. I've taught In 3 different countries, and I currently teach developmental English and English 100-level courses to native speakers and speakers of pidgin, BVE, and various vernaculars. This book is a godsend. I ran across it while in Korea, and I have used it for every class since.
The comma rule simplification in the appendix alone is worth the price of this book. The author breaks all comma rules into 4 basic categories that students can actually understand. Having used books that try to get students to remember 10 + rules for a measly comma, I wish I could kiss the author on the face for making this understandable. It's short enough that students aren't exactly to the REM stage of sleep by the time I'm finished explaining it, but long enough to include all the rules. Some students even actually get it! Hallelujah!
The book also separates organizational tactics (block organization, point-by-point, different types of theses) from grammatical tactics (identifying clauses; frags, ROs, CSs, parallelism; adverbial clauses, etc.), so that you can match chapters to the grammar point - i.e. teach adverbial time clauses with chronological order), or avoid them altogether if you want. The preface offers some suggestions about these types of strategies.
I wish my department would teach with this book, but I don't have tenure so I might as well be begging a wall. If you're contemplating this book or another, get this one.
UPDATE: I got a tenure-track position at a small community college in the U.S. and I'm still using this book. I don't use it as a primary text anymore, but I've not found its equal. It's great for troubleshooting grammatical issues in developmental English classes. When a student comes up to me after class and says, "I just don't get (insert issue not in the scope of the class)," or, "Can I get some extra practice with. . .", I whip out this puppy, look in the index, make a few copies, and BAM, problem solved. Some nontraditional students prefer paper copies, and it's a little more personal than giving them a url and wishing them luck.
The only con is that the layout is dull. Even a font change now and again would liven it up.